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There are 2 lines that run under the bus from the main tank to the aux tank. They should be under a shroud. There is also a balancing line that runs from the top of the main tank, along the side of the tunnel, and into the top of the aux tank. That allows air to be displaced as the aux tank fills from the bottom. Hope that helps!

The tanks are interconnected top and bottom. Gravity just lets the fuel flow where it wants to go.

Don't go into a town in a steep valley with the tank down near a 1/4....

The fuel runs to the back, into the aux, and away from the fuel pick-up in the main tank.

Picturesque little place in La Belle Province has 12 % slope out of town. Back in the day, charter company forbid buying the higher taxed fuel in said province...wait until you cross back into Ontario. So, fuel at the line on the way in, and run the tank almost empty to get out....Sounds good, and many transport outfits did the same thing back before IFTA... It took three different trips, three different out of fuel rescues, with the same coach, to finally discover the driver needed to put $25 of fuel in it, in that town, to make the slope out. And everything was fine from then on.

Serious business when a driver is fired for running out of fuel...all was forgiven...eventually.

Now, keep it in perspective, the fuel wouldn't have been very deep in the regular tank without an aux under this condition. I like a big fuel supply. Aux tanks are great for lengthening the stride of your coach, and give you more choices for where to purchase fuel and how long to boondock on the generator.

However, same as any coach, there are implications if you go mountain goating!

I can personally testify to this fact. I purposely ran low on fuel on a recent trip to burn up some old diesel and planned on getting diesel in Gilroy California. Well, unknown to me being a newbie in an unfamiliar area, I went down a really really steep hill and at the bottom ran out of fuel! I had to call a tow truck driver, and wasnt sure exactly where I was or what the last exit sign said, I told the tow truck driver I needed GAS LOL!! I was parked for about 8 hours with flashers going (hurah for new batteries, I didnt need a jump) and went thru 2 highway patrol officers and 3 different tow truck companies before I got rescued. Oh and it takes 15 gallons to prime, NOT 5

BUT I had just a little under 1/4 tank when I ran out of it in my fuel lines! My bus in an RTS, so I think this may apply to any bus.

« Last Edit: April 28, 2009, 08:37:12 AM by happycamperbrat »

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The Little GTO is a 102" wide and 40' long 1983 GMC RTS II and my name is Teresa in case I forgot to sign my post

So then 1/4 tank should be the least amount one should carry in a coach with an aux fuel tank when going into a hilly area? And does the make, year and model matter? M&C

I think all MCIs are similar, although all do not have the aux. tank. We NEVER let our tank get below 1/4. And, when we add fuel, we fill it full. This helps prevent condensation forming in the tank and contaminating the fuel. If it has an aux. tank it is behind a panel in the center of the front baggage compartment and located against the rear bulkhead of this compartment. Floor to ceiling, approx 2' x 2'. It is inter connected to the main tank underneath the baggage bay floor and an interconnecting vent at the top. It fills when you fill the main tank and feeds the engine at the same time as the main tank. No valves or separate fill. Jack

I think our MCI 7 says including the aux tank it holds 179 gallons (or there about). What is the most fuel anyone has put into an MCI with a aux tank during refueling.

We are about to embark on our 7,500 mile excursion across the country this Friday and just curious about how many actual gallons MCI owners have taken their tanks down to. I usually go down to 1/4 on the fuel gauge but it has never taken 100 gallons to fill it back up. I understand most of the gauges aren't that accurate so I am wary of going much below the 1/4 mark but may be tempted to on this trip just to save some time by eliminating a fueling stop or two.

Our tank capacity, with auxiliary tank, holds 227 gallons. We almost never run out tank down below a quarter tank. We do take advantage of the bigger tanks. Especially when there was the fuel shortage down south earlier this year. We filled up whenever we could, and never had a problem.

I think that the sticker says not to put more than 220 gallons in the tank...how do I figure that out I just fill it up until I can see the fuel .

I have the aux tank in my MC9. I think the most I've ever put in is about 139 gallons last month in WY. Was starting to get a bit worried. Would have to look through my records. there was a time shortly after I bought the coach that I went almost exactly 1000 miles on a tank of fuel. I made the mistake of relying on a gauge that was not functioning properly. I got to my destination thinking I still had 1/8 of a tank of fuel. Unfortunately, I parked on a slight left banking slope and all the fuel ran to the driver's side of the tank. When I started it to go get more, it ran for about 3 minutes. Took me a full day of learning how to reprime it. Fortunately, I had the help of a very famous busnut from the board who just happened to live literally across the road from where we were staying. He shuttled me to town for about 20 gallons and an electric pump to get it going again.

Changed the gauge. Haven't run out of fuel since, but I have do from time to time have issues when it gets down around 1/8 when I go around a right hand corner, such as an interstate on ramp or cloverleaf. Again, all the fuel runs to the left, and I suck air into the intake. About a half mile down the road, the engine starts loosing power and I have to jump out and go switch on the permanently plumbed electric priming pump. Happened more than once. I'm a slow learner.

Dennis, Do you have a separate fuel tank for your generator, Webasto? We are going to install a transfer switch to pump fuel from our main tank to our generator/ProHeat tank, should the need arise. Are you sure the pump is to transfer and not to to prime? Jack

I must admit I ran out of fuel a mile after filling up in Nebraska once. I had a full tank of fuel and lost prime. Cost almost $400 to get roadside service to reprime. My roadside insurance covered it though.

Needless to say two things have happened as a result of this:

1. I learned how to reprime the system myself and I never let the fuel get below 1/4 tank.

2. My wife has retold this story to all my friends and relatives and strangers at RV parks and co-workers and neighbors, in-laws and.....etc.

Between that and the nickname "lo-speed" given to me by some close friends in honor of my assumption that I had an Allison 740 when I really have a 2nd gear start 754 (there is another "phantom" gear past 1rst on the shifter) it's kinda tough on the bus ego sometimes.

My fuel sending unit was bad, so last month i purchased a new one. I installed the new one, and thought it wasnt working, but told myself it was. I dropped a shoestring with a bolt tied to it to check the level, and somehow convinced myself that since the guage was reading 1/2, that there was a 1/2 a tank. Well, the hill 15 miles away reasurred me that the guage was not working! Luckily, my friends house who was coming with us on that tour was within 5 minutes walking distance, so he walked to his house, got his car, drove to the truckstop a few miles away, and 10 gallons of diesel was enough to get us going to the truckstop.

However, I cant really say lesson learned. This rule I tend to violate quite a bit, and I tend to not keep more than about 10 gallons of fuel in my tank. Dont really have a use for it besides to start up and shut off. (That incident i didnt have any WVO in my tanks).

the more empty space inside your fuel tank, the more air volume that breathes in and out by way of expansion and contraction with the heat of the day, the more humidity that gets inside there and you get condensation on the inside walls, which is water, which then runs to the bottom of your fuel tank.

The air in your fuel tank does NOT just stay there, it breathes.

Keep the tanks filled when you are storing the coach in order to defend against water in your fuel.

Water won't run the engine, and depending on the materials in your fuel system, water helps things rust.

;DI just made a deal with Christi, She is in charge of the 1/4 tank alarm system. When ever "I" let the fuel gauge get down to and or below a 1/4, She will start the voical alarm system and starts repeating all the facts from this thread & remind me of all the times "I" ran out of fuel in the SUV, Truck, car, Atv, genny, lawnmower...........I don't think this will work, "I" know it will! All the Best, M&C

;DI just made a deal with Christi, She is in charge of the 1/4 tank alarm system. When ever "I" let the fuel gauge get down to and or below a 1/4, She will start the voical alarm system and starts repeating all the facts from this thread & remind me of all the times "I" ran out of fuel in the SUV, Truck, car, Atv, genny, lawnmower...........I don't think this will work, "I" know it will! All the Best, M&C

I don't know, Jack. It's in the original position of the aux tank and the switch on the eyebrow panel is labeled transfer pump. It's full now, so I'll have to dip the tank after I have used some fuel, and then run the pump and see what's happening.Dennis